Tolerance of rat skin grafts in adult mice.

Adult CBA mice may be made tolerant of August rat tail skin grafts by short intensive treatments with antilymphocyte serum followed by massive ( approximately 100 x 10(6) cells) injections of August rat lymphoid cells. Prolonged tolerance can be achieved only in thymectomized mice, and is accompanied by lymphoid cell chimerism and the manufacture of rat protein. The rat lymphoid cell donors must be treated beforehand with antirat ALS to avoid complications associated with graft versus host reactions. Rejection of rat skin grafts is accompanied by the formation of high titres of antirat hemolysins and lymphocytotoxins, but in "tolerant" mice the rat skin survives in the continual presence of antirat antibodies. Under certain circumstances, however, passive transfusion of high titre mouse antirat serum can precipitate the breakdown of rat skin grafts. It is doubtful if this represents the primary mechanism of rejection. The reaction of normal mice against rat skin is essentially an intensified allograft reaction; it is at all events wholly immunological in character.